1. Field of the Invention
The present invention relates generally to multiple crucible methods of drawing fiber, and particularly to a heating element for a draw furnace for heating a plurality raw materials to be drawn through a multiple crucible into an optical fiber.
2. Technical Background
One common multiple crucible method of drawing an optical fiber is the double crucible method. The double crucible method of forming an optical fiber is disclosed in Optical Fibers for Transmission, New York, John Wiley, pp. 166-178 (Midwinter, 1979), which is hereby incorporated by reference. Inner and outer crucibles are charged with core and cladding glass raw materials. The core and cladding glass raw materials are heated into a molten state. The molten glass may be drawn into a fiber. For additional background on a double crucible apparatus and this method of drawing an optical fiber, reference is made to U.S. Pat. No. 5,106,400, U.S. Pat. No. 4,729,777, U.S. Pat. No. 4,385,916, and U.S. Pat. No. 4,118,212, which are hereby incorporated herein by reference as though fully set forth in their entirety.
A draw furnace will supply the heat to transform the solid glass into a molten state. The draw furnace has a heating element. Two common types of furnace heating elements are an induction element and a resistance element. Known resistance elements have two ends and a respective thick section adjacent each end. The two thick sections are separated by a thin section. The thin section has the highest current density and is the area where the heat is primarily generated. Graphite is a common choice of material of construction for a resistance heating element.